polars.Expr.flatten

Expr.flatten() → Expr

Flatten a list or string column.

Alias for Expr.list.explode().

Deprecated since version 1.38: Expr.flatten() is deprecated and will be removed in version 2.0. Use Expr.list.explode(keep_nulls=False, empty_as_null=False) instead, which provides the behavior you likely expect.

Examples

>>> df = pl.DataFrame(
...     {
...         "group": ["a", "b", "b"],
...         "values": [[1, 2], [2, 3], [4]],
...     }
... )
>>> df.group_by("group").agg(pl.col("values").flatten())  
shape: (2, 2)
┌───────┬───────────┐
│ group ┆ values    │
│ ---   ┆ ---       │
│ str   ┆ list[i64] │
╞═══════╪═══════════╡
│ a     ┆ [1, 2]    │
│ b     ┆ [2, 3, 4] │
└───────┴───────────┘